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Poster: philly_bob Date: Aug 24, 2013 3:06pm
Forum: texts Subject: Copying from 600-ppi scan to 72-ppi screenshot

Consider the following document:

The metadata says it is 600 ppi.

Suppose I want to copy an image from that PDF into my drawing program using the Adobe Reader's "Take a Snapshot" utility. This takes a "snapshot" from my 72 ppi computer screen. Looking at the bottom image on p. 8 (the LA Library), with my Adobe Reader set at 100%, I get a 375 x 534 pixel image in my drawing program.

Am I missing out on some of that 600-ppi scanning resolution in transferring to 72-ppi snapshot? Or do I misunderstand?

Thanks in advance.

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Poster: aibek Date: Aug 26, 2013 12:05am
Forum: texts Subject: Re: Copying from 600-ppi scan to 72-ppi screenshot

The resolution of the original images is indeed 600 ppi. To get better resolution in Adobe Reader try the method mentioned in the section ‘Adjust resolution for copied images’ on the page, with the ‘fixed resolution for snapshots’ set to 600 ppi, obviously. (If it does not work, please tell!)

Even better, though, would be to use the ‘Read Online’ link on the book’s details page. Then,
(i) navigate to the desired page,
(ii) ‘Copy the image location’ in your browser to get link [1], and
(iii) for full resolution, edit [1] to set ‘scale=1’, which gets you [2].

Also, if you intend to rotate the image, and care too much for the resolution, the time to do so will be now (edit the rotate parameter at the end of the url). I am sure that IA will rotate the JP2, and afterwards do the JP2 to JPEG conversion. (In general, any edit of JPEG images -- even cropping -- results in a loss of image quality.)



As for why images acquired directly (via Read Online) are preferable to those extracted from the corresponding PDF file, see link. You would hardly see a difference, but if you care too much for the resolution, acquiring the images directly is certainly preferable.

This post was modified by aibek on 2013-08-26 07:05:24

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Poster: philly_bob Date: Aug 29, 2013 8:03pm
Forum: texts Subject: Re: Copying from 600-ppi scan to 72-ppi screenshot

Thanks, Aibek.

Turns out there are differences between the Adobe Reader 7 menus described in your first link and the Adobe Reader XI I'm using, so I didn't follow through on your first method.

However, your second method, using "Read Online" in the Browser worked just fine. To rephrase your instructions:
(1) Use the Online Reader to find the page with the image you want. Right-click that page and choose "Copy Image Location."
(2) Paste that Image Location URL into your Browser window and go there.
(3) Modify the "Scale" and "Rotate" controls in the URL displayed by your browser. The scale change may not be immediately apparent onscren, because most Browsers automatically resize to fit on screen.
(3) Right-click on the page and choose "Copy Image" to get the image on your Clipboard, then transfer it to the paint program you're using (in Photoshop, New Image/Paste).

Using the "Read Online" method on the L.A. building in the Link in my original post, the image is now 1970 x 2732 pixel instead of the 375 x 534 pixel image I got using Adobe Reader's Snapshot method. Excellent!

As to your comments on editing JPEG files causing loss of resolution, I'm not sure whether that's true if you save as a Photoshop PSD or TIF file. I'll be experimenting to find out.

Thanks for your thoughtful reply. I hope our discussion will be useful to others.


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Poster: aibek Date: Aug 30, 2013 6:17am
Forum: texts Subject: Re: Copying from 600-ppi scan to 72-ppi screenshot

Hello philly_bob

Taking a JPEG and after processing saving it as JPEG would, in general, cause a little loss of image quality. That is because unless the image has certain special properties the image processor † which is saving it as jpeg would do the quantization anew (and not use the quantization of the original image). I doubt that it matters in practice; I mentioned it just to make sure that you know about it.

The issue effects only JPEG. PSD or TIFF (or other lossless compression formats) would of course be free of it, but at the cost of much greater file size!

Please check this link:

† There are special programs which take the inner workings of JPEG into account to do lossless transformation. The one popular in GNU/Linux world is jpegtran. (Windows version is available too.)
For other programs check this:

This post was modified by aibek on 2013-08-30 13:17:38